This title is fourth in a series of pamphlets on the Mexican War, which was the U.S. Army's first experience waging an extended conflict in a foreign land. This brief war is often overlooked by casual students of history since it occurred so close to the American Civil War and is overshadowed by the latter's sheer size and scope. Yet, the Mexican War was instrumental in shaping the geographical boundaries of the United States. At the conclusion of this conflict, the U.S. had added some one million square miles of territory. The Mexican War still has much to teach us about projecting force, conducting operations in hostile territory with a small force that is dwarfed by the local population, urban combat, the difficulties of occupation, and the courage and perseverance of individual soldiers.